Diorganomagnesium compounds are well known for their usefulness in a wide variety of chemical reactions. As reagents, these compounds can be used for the alkylation of ketones and the alkylation of metal halides or oxides to the corresponding metal alkyls. As catalysts, diorganomagnesium compounds are useful in the dimerization and polymerization of olefins, see Britain Pat. No. 1,251,177, the polymerization of epoxides, see U.S. Pat. No. 3,444,102, and the preparation of telomers, see U.S. Pat. No. 3,742,077. While they perform many of the same types of functions performed by Grignard reagents, diorganomagnesium compounds, owing to differences in electronic and steric factors, are more reactive than Grignard reagents toward certain types of compounds. In general, see also U.S. Pat. Nos. 3,646,231 and 3,822,219.
The utility of diorganomagnesium compounds is lessened by the fact that many are either solids or highly viscous liquids. This problem is generally overcome either by dissolving the compound in an inert hydrocarbon solvent or by solvating the compound. All are unstable upon exposure to moisture and air and require handling under an inert atmosphere. Some diorganomagnesium compounds, with straight chain lower alkyl groups of up to four carbon atoms, are insoluble by themselves in hydrocarbon solvents and thus require solubilizing agents which will form a soluble complex. Examples of such solubilizing agents are alkyllithium compounds, see U.S. Pat. No. 3,742,077, dialkyl zinc compounds, see U.S. Pat. No. 3,444,102, alkali metal hydrides, see U.S. Pat. No. 3,655,790, and organoaluminum compounds, see U.S. Pat. Nos. 3,737,393 and 3,028,319, and combination of certain dialkylmagnesium compounds in hydrocarbon solvents. See. U.S. Pat. Nos. 4,069,267 (C.sub.1 to C.sub.4 di-n-alkylmagnesium and C.sub.6 to C.sub.18 dialkylmagnesium), 4,127,507 (di-n-butyl magnesium and di-ethyl magnesium), 4,207,207 (di-methylmagnesium and di-n-propyl magnesium) and 4,222,969 (dimethylmagnesium and di-n-butyl magnesium).
Solvation involves the use of an ether or other organic Lewis base molecule to associate directly with the magnesium atom, thus yielding a hydrocarbon soluble complex. The solvated form is undesirable however, since solvation seriously inhibits the effectiveness of the compound, for some uses, particularly when the compound is used as a Ziegler-type polyethylene catalyst. The use of ether is particularly undesirable because it is flammable and its vapors are explosive. Also, it introduces soluble RMgX according to the Schlenk equilibrium EQU R.sub.2 Mg+MgX.sub.2 .revreaction.2RMgX
where R is alkyl and X is halogen.
Solubilization also serves to reduce the viscosity of reaction mixtures whose high viscosity would otherwise inhibit the stirring of the reaction mixture and cause difficulty in handling and transferring. This problem is only partially solved by the use of chloroaryl solvents to form low viscosity suspensions of the insoluble compounds, as described in U.S. Pat. No. 3,264,360.
In addition, the insolubility of the lower alkyl magnesium compounds makes preparation of them in a form free of undesirable co-product magnesium halides difficult. In particular the direct reaction of magnesium metal with an organic halide is disclosed in Glaze and Selman, Journal of Organometallic Chemistry, Vol. 5. p. 477 (1967), and W. N. Smith, Journal of Organometallic Chemistry, Vol. 64, p. 25 (1974). These articles deal with the preparation of diorganomagnesium compounds with straight chain alkyl groups of 5 carbon atoms and higher. Such compounds are soluble in hydrocarbon solvents and thus readily separable from the concurrently produced magnesium halide and unreacted magnesium. When lower straight chain alkyls are used in this process, the desired diorganomagnesium compound is formed but is insoluble and exists as a slurry in the solvent together with the magnesium halide and unreacted magnesium metal. Thus a solubilizing agent is required when this process is used to make lower alkyl diorganomagnesium compounds. The latter are particularly desirable as reagents and catalysts owing to their relatively high magnesium content on a weight basis.
Other methods of preparation include the mercury-magnesium exchange method, as disclosed in Cowan and Mosher, Journal of Organic Chemistry, Vol. 27, p. 1 (1962), and the dioxanate-precipitation method, as disclosed in Schlenk, Berichte der Deutschen Chemischen Gesellschaft, Vol. 64, p. 734 (1931). The mercury method, EQU R.sub.2 Hg+Mg.fwdarw.R.sub.2 Mg+Hg
where R is alkyl, is limited by the high cost of dialkylmercury compounds, and the health hazards involved in their use. The reaction itself is hazardous since it proceeds rapidly and exothermically after an inhibition period.
The dioxanate-precipitation method, ##STR1## where R is alkyl and X is halogen, involves removal of magnesium halide from ether solutions of Grignard reagents by precipitation of a complex which the dioxane forms with the halide. This is a tedious process and results in an etherated dialkylmagnesium complex from which the ether must be removed prior to use as a catalyst component in Ziegler type polymerizations.
Dialkylmagnesiums ca also be prepared from alkyllithiums, see U.S. Pat. No. 3,646,231 by precipitation of lithium halide, EQU MgX.sub.2 +2Li.fwdarw.R.sub.2 Mg+LiX
where R is alkyl and X is halogen. This process is unsuitable for straight-chain lower alkyl diorganomagnesiums which are insoluble in hydrocarbon solvents, since separation from co-product lithium chloride will be impossible. The use of basic solvents renders separation possible but requires subsequent desolvation. U.S. Pat. Nos. 4,127,507; 4,207,207 and 4,222,969, each state that branched chain diorganomagnesium compounds cannot be prepared by the Glaze and Selman method, i.e. the direct reaction of magnesium metal with an organic halide. U.S. Pat. No. 4,069,267 further confirms this wherein it is stated that when pure, dry metallic magnesium is treated with an alkyl halide, in a liquid hydrocarbon solvent such as heptane, cyclohexane, or toluene, it is found that only certain alkyl halides, those of the normal or unbranched variety, e.g., n-butyl chloride react to produce the desired dialkylmagnesiums. Thus, resort to the lithium halide precipitation method is required.
The general insolubility of straight chain lower alkyl magnesium compounds is thought to be due to intermolecular association resulting in the formation of a polymer-type macrostructure wherein each magnesium atom is tetrahedrally surrounded by four short alkyl groups. Known methods of solubilizing these compounds presumably operate to break some of the intermolecular bonds and thereby break down the macro-structure into shorter, more soluble units. Solvation or complexing as described above are thought to bring about this effect.
Alkylmagnesium compounds containing either branched chain alkyl groups or straight chain alkyl groups of five carbon atoms or more, known to be effective as solubilizing agents, may operate by breaking the intermolecular bonds. Probably, the effect occurs by way of alkyl interchange and re-association, whereby the solubilizing alkyl groups exchange positions with some of the straight chain lower alkyls. Solids formation is thus sterically hindered, either because the substituted groups are unwieldy in solids packing, or because the groups have some inherent solubility of their own.
W. Novis Smith, Jr. in the Journal of Organometallic Chemistry 64 (1974) pp. 25-40, page 29, states that many attempts were made to obtain sec-dialkyl magnesium compounds in hydrocarbon solvents using the direct reaction of sec-alkyl halide and magnesium, but only very low concentrations were ever obtained and that these were with sec-alkyl iodide in benzene. A small amount of precipitate always formed.
It has been discovered that although branched chain organo magnesium compounds cannot be made from magnesium metal and branched alkyl halides in a hydrocarbon solvent when the halide is 2-halobutane or iso-butyl halide, they can be made from 3-methyl-1-halo-butane (isoamylhalide), or other remotely branched chain alkyl halides.
It is therefore an object of the present invention to provide hydrocarbon-soluble diorganomagnesium compositions of high magnesium content.
A further object of the present invention is to provide a process by which hydrocarbon soluble diorganomagnesium compositions of high magnesium content can be prepared by the direct reaction of alkyl halides with magnesium.
A still further object of the present invention is to provide a means for solubilizing straight chain lower alkyl diorganomagnesium compounds in hydrocarbon solvents.
Another object of the present invention is to provide a composition of matter comprising di-isoamylmagnesium, diethylmagnesium, and a hydrocarbon solvent.
Yet another object of the present invention is to provide a process for the manufacture of unsolvated branched-chain, lower alkyl diorganomagnesium compounds, namely diisoamylmagnesium.